"truncate table ECSCDAP1P.alan;" removes all rows from the table and its indexes and removes all extra extents from the table and all its indexes. Truncate table also has the added benefit of not generating a lot of redo logs but will eliminate all rows completely and no rolling back.

"alter table ECSCDAP1P.alan move online;" moves and shrinks the table but invalidates its indexes so the application goes down (if indexes exist on the table).

"alter table ECSCDAP1P.alan shrink space;" moves and shrinks the table and does not leave any indexes unusable so the application never has an outage. Indexes can then be rebuilt online if you want to reclaim the space from the indexes.